1. Field of the Invention
The present invention relates to a step motor drive unit and an analog electronic timepiece in which a display hand is rotation-driven by the step motor drive unit.
2. Description of the Prior Art
From old times, there is utilized the analog electronic timepiece in which the display hand such as hour hand and minute hand is rotation-driven by the step motor drive unit. The step motor drive unit has a step motor and a drive circuit for rotation-driving the step motor.
The step motor has a stator having a rotor accommodating through-hole and a positioning part for determining a stop position of a rotor, the rotor rotatably disposed in the rotor accommodating through-hole, and a coil wound in the stator. There is adapted such that, by alternately supplying a drive pulse whose polarity differs to the coil from the drive circuit, a magnetic flux whose polarity differs is alternately generated in the stator and, by this, the rotor is rotated in a predetermined, same direction by a predetermined angle at a time and the rotor is stopped in a position corresponding to the positioning part.
As to a rotation drive of the step motor, there are demanded an energy saving and a certainty of the rotation drive. For this reason, under a normal state, the rotor is previously rotation-driven by the drive pulse of a predetermined energy (e.g., drive pulse of a predetermined width (normal drive pulse)) and, in a case where the rotor is not rotated by the rotation drive by the normal drive pulse, the rotation drive is performed by supplying the drive pulse (correction drive pulse) whose energy is higher (e.g., wider in pulse width) than the normal drive pulse. By this, the energy saving is made possible, and there is constituted such that the rotor can be certainly rotated (e.g., refer to JP-B-63-18148 Gazette, JP-B-63-18149 Gazette, JP-B-57-18440 Gazette).
In such a step motor drive unit driven by a small energy as mentioned above, the step motor is driven by plural drive pulses. However, when the rotor has not been rotated by the normal drive pulse, since the motor is rotated by the correction drive pulse, a remanent magnetism of the stator is demagnetized only when rotation-driven by the correction drive pulse, so that a demagnetization pulse whose polarity differs from the correction drive pulse is supplied to the coil.
FIG. 7 is a timing diagram of the conventional step motor drive unit, and is a diagram showing voltage waveforms of both terminals a, b of the motor.
In FIG. 7, under a normal state that a rotation drive operation is normally performed, by alternately supplying a normal drive pulse P11, of a predetermined pulse width, whose polarity differs to the terminals a, b of the motor, the rotor is rotated.
Like FIG. 7A, in a case where the motor does not rotate even if rotation-driven by the normal drive pulse P11, in a rotation detection term Tk since there is not detected a rotation detection pulse Sr higher than a predetermined level, it is judged that the motor is not rotating in the step motor drive unit.
In this case, after a predetermined term has elapsed after driving by the normal drive pulse P11, the motor drive unit rotation-drives the motor to thereby forcibly rotate it by a correction drive pulse P2 (constituted by a pulse portion P21 for the rotation drive and a braking pulse portion P22 for giving a braking to a vibration after a rotor rotation) whose pulse width is wider than the normal drive pulse P11 and, after a predetermined term has elapsed, supplies a demagnetization pulse Pe, whose polarity is reverse to the correction drive pulse P2, in order to demagnetize the stator having been magnetized by the drive by the correction drive pulse P2.
By this, even in a case where the rotor is not rotated by the normal drive pulse P11 owing to an increase in load and the like, it is possible to rotate the rotor by the correction drive pulse, and it becomes possible to prevent a generation of a rotation abnormality owing to a magnetization of the stator, and the like.
Next, as shown in FIG. 7B, there is rotation-driven by a normal drive pulse P12 whose width is wider by a unit pulse width Pt than the normal drive pulse P11. By this, if the rotor rotates, in the rotation detection term Tk there is detected the rotation detection pulse Sr higher than the predetermined level. By the detection of the rotation detection pulse Sr, the step motor detection unit judges that the motor has rotated. Hereafter, during the motor is normally rotating, the motor is rotation-driven by alternately supplying the normal drive pulse whose polarity differs.
By doing like the above, even in a case where an abnormal state and the like have occurred, although it is possible to rotate the motor, in a case where the correction drive pulse P2 has been outputted, the demagnetization pulse Pe must be also outputted for the stator demagnetization. That is, in the conventional step motor drive unit, since it is necessary to generate three kinds of pulses of the normal drive pulse, the correction drive pulse and the demagnetization pulse, there is a problem that a circuit constitution becomes complicated and becomes expensive.
Further, unless the demagnetization pulse Pe is outputted after a vibration of the rotor has subsided, an effective demagnetization is not performed. Accordingly, when outputting the demagnetization pulse Pe, since there is a restriction in time, there is a problem that the circuit constitution becomes complicated and thus a reduction in integrated circuit (IC) chip size is difficult, and further becomes expensive one. Further, there is a problem that a high speed drive is impossible.
Additionally, an inspection of whether the demagnetization pulse Pe is being normally outputted becomes also necessary and, from the fact that the inspection is outputted with the polarity reverse to the correction drive pulse P2, there is a problem that the IC becomes more complicated.
The present invention is one made in order to solve the above problems, and its problem is to make it possible by a simple constitution to perform a forcible rotation drive by the correction drive pulse and obtain a demagnetization effect.